1. Field of the Invention
The present invention broadly relates to an expandable mandrel or plug especially adapted to securely hold a rubber surfaced roller of a printing press on a lathe in accurate, precise alignment with centers of the same so that the rubber surface of the roller can be ground to dimensions within extremely close tolerances. More particularly, the invention concerns a grinding plug formed of a body having resilient, sector-shaped segments which flex outwardly to engage an interior wall of the press roller; the body is of a particular configuration which ensures that all of the segments shift an equal distance during flexing to maintain the central axis of the lathe centers in perfect alignment with the longitudinal axis of the roller.
2. Description of the Prior Art
Rubber-surfaced rollers of a printing press must be reconditioned from time to time after periods of extended use. In normal practice, the roller is removed from the press and sent to a reconditioning facility where the old and worn rubber material surrounding the metallic roller is removed. Next, a new section of rubber is affixed to the metal cylinder by glue or other means.
However, special precautions must be taken to ensure that the outer surface of the rubber is in the shape of a true cylinder that is concentric with the central axis of the roller. To this end, the roller is typically mounted on a lathe and the outer surface of the new rubber section is ground to a smooth cylindrical configuration. Press manufacturers often specify, in this regard, that the finished rubber outer surface should be concentric with inner cylindrical walls of the roller which normally receive the roller bearings to a dimension of 0.001 inch.
In accordance with conventional practice, bearings within the printing press rollers are often replaced at the same time that the rubber rollers are taken out of service for resurfacing. Consequently, the rollers are shipped to the reconditioning facility without bearings, and personnel at the reconditioning facility must then press in new bearings compatible with the lathe so that the roller may be held in alignment with the centers of the lathe. Once the resurfacing operation is completed, the bearings are then removed by a second pressing operation before the roller is returned to the location where the printing press is in service. As can be appreciated, the steps in pressing in and pressing out of temporary bearings for supporting the roller during the resurfacing and machining process represent an expenditure which significantly increases the overall cost of the reconditioning operation accordingly.
As a result, it would be a desirable advance in the art to provide a device which could be readily inserted by hand into the hollow ends of a printing press roller, and yet would be operable to securely hold the roller without slippage once mounted on centers of a lathe. Moreover, and of equal importance, is the need for such a device to securely retain the longitudinal axis of the cylinder in precise alignment with the centers of the lathe, so that tolerances of less than 0.001 inch during machining of the outer rubber surface can be achieved.